What if Romeo and Juliet had lived? What if Romeo had been waiting there when Juliet awoke in the tomb, and the two of them had giddily eloped to Mantua, to live happily ever after? They wouldn't have any money. Romeo would need to get a job. Juliet would stay at home all day, afraid that her family would find her if she dared to venture out. Alone at home, she'd be bored out of her skull. She'd want Romeo to stay home for sex and conversation every day. Both of them had grown up in wealthy families, and were used to the finer things in life. Juliet would grow increasingly impatient at her new standard of living. She'd start peeking out of the window, wanting to escape the little domestic box in which she'd been entombed alive. One day, a rich older man would see her at her window. She would look at him, looking at her. It's so much easier to love "till death do us part" if death parts us quickly.

Thomas Middleton's Women Beware Women is Romeo and Juliet for grown-ups. It begins pretty much where Shakespeare's vision of breathless adolescent romance ends: with a newly married couple, eloped from Venice, arriving in Florence. The husband's tragic mistake is to go to work. Young, horny Leantio would like to stay at home all day in bed with his bride, Bianca. But he decides to be responsible: "Man loves best/ When his care's most." Historically, most husbands have been cuckolded when they are away at work, doing their breadwinner duty. It happens even now. And any modern victim will recognise the painful bitterness of Middleton's irony.

The 16-year-old wife's tragic mistake is to listen to the older women whom society tells her to trust. Listening to her mother-in-law's criticisms of her sentimentality, she lingers on the balcony for a few minutes after hubby leaves. The Duke of Florence, parading by, sees her there. Arrangements are made for an older female neighbour to lure Bianca out of the house, and then to be trapped by the Duke. Imagine Juliet's nurse setting her up to be raped by the Prince of Verona, and you'll understand one reason for the play's politically incorrect title: Women Beware Women.

Bianca doesn't kill herself because she's been raped. That's what a classically virtuous wife is supposed to do: that's what happens in Shakespeare's Lucrece. Bianca's reaction is more complicated than that. She's not sure what she feels, in fact, or how she should feel, or what she should do. There's no one she can talk to. She's afraid she's pregnant. She becomes irritable, demanding, bitchy. When her husband returns from work at the end of the week, he expects: "A kiss now that will hang upon my lip/ As sweet as morning dew upon a rose." She isn't in the mood. "We have been married," she reminds him, "a whole fortnight now." Ouch. The honeymoon is over.

Most honeymoons don't end with the bride being raped by the country's most powerful politician. But the honeymoon does always end, one way or another. "'Tis tedious to see one thing still, sir/ Be it the best that ever heart affected," she tells him. "As good be blind, and have no use of sight/ As look on one thing still." This is something most wives (or husbands) don't have the courage or the cruelty to say - but if you have ever been in a relationship that lasted more than two weeks, you know it's true.

It takes Middleton only three-and-a-half scenes to get to this point in the tragic love story of Leantio and Bianca. Life moves brutally fast sometimes, doesn't it? Especially in cities. Population density increases the number of potential personal interactions, and the rapidity with which they tumble and pile up against each other. It's no accident that a lifelong Londoner wrote: "Hurry, hurry, hurry!" That motto of the modern world, written in 1606, comes from Middleton's The Revenger's Tragedy, which, like Women Beware Women, was inspired by 16th-century Florentine history. Italian city-states were the first modern commercial urban centres; Italy was then the slick man of Europe, racing into the future faster than anyone else.

Like all Middleton's tragedies, Women Beware Women keeps going at this ferocious emotional pace. These are fast people, living in fast times. The Duke's rape of Bianca takes three minutes of stage time. By the fifth scene of her story, she is being publicly displayed as the Duke's mistress. The innocent romantic bride - Middleton's Juliet - has become what we would call a "fast woman".

In 1963, the critic Kenneth Tynan declared that: "Where sexual vagaries are concerned there is more authentic reportage in The Changeling and Women Beware Women than in the whole of Shakespeare." Those two plays are typical. Middleton packed more sexual variety into his work than any other writer in English. Women Beware Women includes, aside from the Bianca plot, a compellingly believable and emotionally complex story of incest. A mother tries to prostitute her daughter in The Revenger's Tragedy. Necrophilia takes centre stage in The Lady's Tragedy. A royal husband forces his wife to eat the corpse of her adulterous lover in The Bloody Banquet. In Hengist, King of Kent a husband has his wife abducted and blindfolded so that he can sadistically rape her (since she doesn't know it's him); he does it in front of another man. Middleton's no-holes-barred sexual imagination was at least as comprehensive as Freud's, and more varied, tonally, than the repetitive mathematical porn of writers like Sade.

Which explains why we prefer Shakespeare in our classrooms. Romeo and Juliet - especially in the sanitised, bowdlerised textbooks used in most schools - is more romantic. More monogamous. More Hollywood. Whether that kind of romantic myth does kids any good, in the long run, is another question. It certainly didn't do Bianca and Leantio much good.

First love is an intense experience. But it is not our only experience. I adored Romeo and Juliet when I was a teenager. But it's been a while since I was a teenager. Now, I wouldn't cross the street to see Romeo and Juliet. But I'd cross the Atlantic to see Women Beware Women.